Finishing line heat recovery

ABSTRACT

An article finishing line and coating system including a spray washing station for washing the articles with heated liquid and a coating station, between a drying oven for drying the washed articles and a curing oven for curing the coating which is applied to the articles at the coating station. The washing liquid is heated in tanks having immersion conduits therein heated by infrared burners and the exhaust gases from the immersion heaters are conducted to the curing oven, both directly and by way of the drying oven, to supplement the heat requirements of these two ovens.

ilnited ttes atent Wick et al.

14 1 Feb. 11, 11975 FINISHING LINE HEAT RECOVERY [75] Inventors: Richard G. Wick, Downers Grove; 'f Stem Henry J. Bennett, Palos Park both Assistant Examiner-Douglas Salser of m Attorney, Agent, or Firm-Mol1nare, Allegretti, Newitt & Witcoff [73] Assignee: Burdett Manufacturing Company,

Bridgeview, Ill. [57] ABSTRACT [22] Filed; Aug. 27, 1973 An article finishing line and coating system including a I spray washing station for washing the articles with I Appl' 39l73l heated liquid and a coating station, between a drying oven for drying the washed articles and a curing oven [52] us. Cl. 118/66 for ng the ating hich is applied to the articles [51] Int. Cl. B05C 11/00 at h ating ation. The washing liquid is heated in [58] Field of Search 1 18/66, 67 tanks h ing imm r ion con its therein heated by infrared burners and the exhaust gases from the immer- [56] R f nce Cit d sion heaters are conducted to the curing oven. both UNITED STATES PATENTS directly and by way of the drying oven, to supplement 2,378,758 6/1945 Ekstrom 118/66 the heat requ'remems of these two Ovens 3,265,033 8/1966 Touze et a1, 118/67 15 Claims, 3 Drawing Figures 62 A. 5 c 60 68 CURING OVEN A 70 I 738 J 5o 54 AUTOMATIC MANUAL COATING COATING I I8 20- 3 151? SPRAY wAsHER IST STAGE 2ND STAGE n 2o 3RD STAGE g 1' L LOAD ----UNLOAD FINISHING LINE I-IEAT RECOVERY BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to an article finishing line and coating system and, more particularly, to an article coating system in which substantial quantities of heat may be recovered and reused in the system.

Article coating and finishing lines have attained widespread use in the automated coating of numerous and varied articles, e.g. cookware containers and the like. In such systems the article to be coated is positioned on a moving work holder at a load station and the work holder and article are conveyed to a spray washer. The spray washer generally includes one or more stages for the removal of manufacturing lubricants and the pretreating of the metal to be coated to make the metal surface more receptive to the coating. From the washer, the articles are conveyed to a drying oven where the articles are dried, to a coating station where the articles are coated by spraying, dipping or the like, and then to a curing oven where the coating is cured. During operation each of the spray washer and the drying and curing ovens consume substantial quantities of heat. Heretofore, the exhaust from the washer and the ovens, and the heat remaining therein, has generally been discarded after use in the respective components, except that, in a few installations, the exhaust heat from the spray washer has been utilized to some extent in supplementing the heat requirements of the drying oven. The exhaust from these various coating system components has not generally been recovered, with the exception last noted, for several reasons. The principal reason is that these exhaust gases are frequently contaminated with noxious gases and/or particulates such as would damage the coating being cured in the curing oven and might be toxic to personnel in the areas surrounding the ovens. The coating systems in the past frequently relied upon open flame burners to supply the required heat, both in the immersion conduits in the washing liquid tanks, as well as in the ovens. Such flame burners are susceptible to quenching which results in the production of substantial quantities of aldehydes and carbon monoxide which become entrained in the exhaust gases. These contaminants have a detrimental effect on the coatings if they are allowed to contact the coatings. The probability of quenching in such flame burners is particularly high where the burners are in immersion conduits, such as in the washer, since the flame contacts the relatively cold walls of the conduit. Moreover, quenching also occurs in the flame burners in the drying and curing ovens whenever the flame is located in an area of high air velocity, as it frequently is.

Rich fuel to air mixtures frequently result in the generation of soot which detrimentally effects coating quality, whether the soot is deposited on the articles in the drying or the curing oven. This is particularly a problem in the immersion conduits of the washer, since there is no secondary air present to insure complete combustion in the event that insufficient air is mixed with the fuel introduced to the flame burners. To reduce the likelihood of such sooting, these flame burners are usually fed lean mixtures. However, sooting will still occur if this mixture is accidentally altered or if the air and fuel metering and mixing devices become worn from use.

It is one of the principal purposes of the present invention to provide an article finishing line and coating system in which the exhaust gases from one or more of the spray washer immersion heaters and/or the drying oven may be recovered for use in supplementing the heat requirements of the drying oven and curing oven, respectively. In the finishing line and coating system of the present invention, efficient infrared burners are employed in the immersion heaters of the spray washer of the system resulting in the production of exhaust gases which are substantially free of detrimental contaminants and which may be recovered for use in one or both of the drying oven and the curing oven. In the system of the present invention, the exhaust gases from the heat sources of the several components are placed in direct contact with the articles. Finally, in the system of the present invention, infrared burners may also be employed in the drying oven and curing oven as the primary heat sources for these ovens.

In a principal aspect of the present invention, an arti' cle finishing line and coating system includes a spray washing station, a tank for containing the washing liquid having immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, and conveyor means for conveying the articles between the stations. In combination therewith, conduit means conducts the hot exhaust gases from the immersion conduit means to the curing oven such that these hot exhaust gases are utilized to cure the coating on the articles.

In another principal aspect of the present invention, the aforementioned system also includes a drying station and a portion of the hot exhaust gases from the immersion conduit means is conducted directly to the curing station while another portion is conducted to the drying station and then to the curing station in parallel relationship with the first portion.

In still another principal aspect of the present invention, infrared burners are employed in one or more of the immersion conduit means, the drying station, and the curing station.

These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS In the course of this description, reference will frequently be made to the attached drawings in which:

FIG. 1 is an overall schematic view of an article finishing line and coating system incorporating the principles of the present invention;

FIG. 2 is a cross sectioned plan view of one of the liquid heating tanks of the power spray washer of the system, as viewed substantially along line 2 2 of FIG. 1; and

FIG. 3 is a cross sectioned end elevation view of the drying oven of the system, as viewed substantially along line 3 3 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring particularly to FIG. 1,. an overall schematic view is shown of a preferred embodiment of article finishing line and coating system incorporating the principles of the present invention. The system includes a load station at which the articles to be finished and coated are introduced to the system onto a conveyor 12. The conveyor 12 is shown schematically in FIG. 1 by a dot and dash line.

The individual articles are loaded onto work holders on the conveyor and are conveyed into a power spray washer 14 having one or more stages. Three stages l6, l7 and 18 are shown in FIG. 1. In the first stage 16 the articles are washed with heated liquid containing suitable detergents to remove manufacturing contaminants, such as lubricants, metal filings and the like, from the articles. The articles then move to the second stage 17 where the articles are rinsed, and then to a third stage 18 where the articles may be pretreated with heated treating solutions for the purpose of preparing the metal surfaces for receipt of the coatings, such as mild acid etches and the like.

Each of the stages 16, 17 and 18 includes a suitable manifold 20 having spray nozzles 22 arranged along the manifolds in locations depending upon the configuration of the articles to be treated. The washing liquids are contained in separate tanks 24, 25 and 26 at the bottoms of the respective stages l6, l7 and 18. The liquids are pumped from these tanks to their respective manifolds 20 by way of suitable pumps (not shown).

The washing liquids in the tanks 24 and 26 of the first and third stages 16 and 18 are preferably heated by way of submerged serpentine immersion conduits 28 through which heated exhaust gases pass to heat the liquid. The hot exhaust gases are produced by one or more fuel burners 30 which may be arranged either in the immersion conduit itself, or in a submerged heating box 32 at the lead end of the conduit 28. Box 32 is also preferably completely submerged in the washing liquid in the tank, the liquid completely surrounding the box. A mixture of fuel and oxygen is fed to these burners in the correct proportions to sustain combustion at the burners.

It is preferred that the burners 30 be of the infrared type, since such burners not only operate at higher temperatures, on the order of 1,600 2,300 F, but also the flame may be readily controlled to prevent it from impinging the walls of the immersion box 32 and conduits 28. Thus, infrared burners not only result in more efficient and complete combustion, but also they are less prone to quenching. These advantageous operating characteristics of infrared burners substantially reduce the likelihood of presence of objectionable contaminants and soot in the exhaust gases, since the exhaust gases produced consist essentially of the pure combustion products of carbon dioxide and water only. Moreover, infrared burners also produce lower levels of oxides of nitrogen than typical open flame burners.

Once the articles have been prepared in the power spray washer 14, they are conveyed to a drying oven 34 having several burners 36 therein, also preferably of the infrared type. These burners 36 are preferably located adjacent the bottom of the oven 34 to minimize the possibility of quenching, since air velocities are usually relatively low in this region. In the drying oven 34 sufficient heat is introduced to dry the washed articles prior to coating the articles. The drying oven 34 includes one or more ducts 38 at the top of the oven from which heated air and gases are removed from the oven and pumped, by way of blower 40, back to supply ducts 42 extending longitudinally just above the burners 36. This air is then discharged from bottom openings 44 in the supply ducts across the burners 36 as shown in FIG. 3, the air being heated as it flows over the burners. The heated air then circulates upward and passes over the articles being dried, which are conveyed on the conveyor work holder 46, and the air is withdrawn and again recirculated through the ducts 38. The drying oven may be maintained at temperatures 400 450 F by way of example. These temperatures are generally sufficient to raise the temperature of the articles to 200 220 F in a relatively short time to evaporate the water remaining on the articles after washing.

One of the principal features of the present invention includes the provision for recovering the exhaust gases from the first stage 16 of the power spray washer immersion heater 28 and conducting these gases, by way of conduit 48, for stimultaneous introduction into the air recirculation system of the drying oven 34 along with the air which is recirculated by way of blower 40 through conduit 50. Thereby, these already heated exhaust gases from the first stage immersion conduit, rather than being discarded and wasted, are introduced to the drying oven where they are reused to supplement the heat introduced by the burners 36, reducing the amount of heat which must be supplied to the oven by the burners. As shown in FIG. 1, conduit 48 communicates with the supply ducts 42. In the alternative, conduit 48 may communicate directly with the suction side of blower 40.

After the articles have been dried, they are conveyed to an automatic coating station 52 where the articles are coated. If necessary, the articles then pass to a manual coating station 54 where any misses" may be manually touched up. From the manual coating station 54 the articles are conveyed to the curing oven 56 where the articles are exposed for a time and at a temperature sufficient to cure the coating. The temperature of the curing oven typically ranges between 300 450 F, although it may be higher or lower depending upon the type of coating being cured.

The construction of the curing oven 56 is substantially identical to that of the drying oven 34. The curing oven 56 includes a recirculation system including one or more ducts 58 at the top thereof, a pair of supply ducts 60 toward the bottom thereof, and a plurality of burners 62 are positioned at the bottom of the oven. Again the burners 62 are preferably infrared burners. A blower 64 is provided at the top of the curing oven to remove heated air and gases and recirculate the air and gases to the supply ducts 60 by way of conduit 66. From the supply ducts, the air and gases are discharged, as previously described with respect to the drying oven 34, over the burners 62 which add the heatnecessary to maintain the oven at the desired temperature.

Again a principal aspect of the present invention resides in the recovery and reuse of heated exhaust gases, in this instance, both from the power spray washer 14, as well as the drying oven 34.

The heated exhaust gases from the immersion conduit 28 of the third stage 18 of the power spray washer 14 are conducted directly, by conduit 68, to the curing oven air recirculation system and are mixed with the air and gases recirculated by blower 64 and conduit 66. In addition, the still heated excess exhaust gases from the drying oven 34 are drawn off the drying oven by way of an exhaust blower 45 and pass, by way of conduits 70, to the air recirculation system of the curing oven 56. Again it will be understood that although the conduit 70 is shown in FIG. I as discharging directly to the supply ducts 60, conduit 70 may be connected to the suction side of recirculation blower 64. It will therefore be seen that recirculated gases from the curing oven itself, by way of conduit 66, gases directly from the immersion conduit 28 of the third stage 18 of the power washer, by way of conduit 68, and gases from the first stage 16 of the power washer, by way of conduit 48, drying oven 34 and its ducts 38, blower 45 and conduit 70, all mix in the air system of the curing oven and these already heated gases are discharged across the burners 62 of the curing oven to reduce the heat input which would otherwise be required of these burners.

Blower 45 on the drying oven 34, not only positively draws air from the drying oven and introduces this already heated air to the air recirculation system of the curing oven 56, but also insures against the buildup of high concentrations of water vapor which otherwise might impair the drying process. In addition, blower 45 insures against the buildup of any undesirable noxious or toxic gases in the drying oven 34.

A second blower 72 is also provided on the curing oven 56. Blower 72 has the purpose of removing a predetermined portion of the heated gases and discharging these gases from the system. Such removal prevents the buildup of noxious, toxic or explosive components in the gases, such as evaporated coating solvents, and also creates a slight negative pressure throughout the entire exhaust system, thereby preventing the accidental leakage of potentially harmful exhaust gases into the surrounding work areas.

The heat recovery which may be effected in a system employing the principles of the present invention may result in as much as 20% reduction in the total fuel requirements of the system.

As employed herein, the infrared burners are generally of the type in which the burning fuel heats a suitable refractory, which refractory then radiates the principal portion of the heat as radiant, infrared heat. Suitable infrared burners for use as one or more of the burners 30, 36 and 62 are available from Burdett Manufacturing Company, Chicago, Illinois.

It will be understood that the embodiment of the present invention which has been described is merely illustrative of one of the applications of the principles of the invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.

What is claimed is:

1. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the Washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, conveyor means for conveying the articles between said stations, and a drying station along said conveyor means between said spray washing station and said coating station, wherein the improvement comprises in combination therewith:

conduit means for conducting the hot exhaust gases from said immersion conduit means to said curing oven wherein said hot exhaust gases are utilized to cure the coating on the articles and to said drying station to dry the articles prior to coating, said conduit means also conducting hot exhaust gases from said drying station to said curing station wherein the hot exhaust gases from said drying station are utilized to cure the coating on the articles. 2. The system of claim 1 wherein said conduit means conducts a first portion of said hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion.

3. The system of claim 2 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.

4. The system of claim 1 including infrared fuel burners in said immersion conduit means, said hot exhaust gases being the exhaust gases of burners.

5. The system of claim 1 including heat generating means in said curing station, said hot exhaust gases supplementing the heat generated by said heat generating means.

6. The system of claim 5 wherein said heat generating means comprise infrared fuel burners.

7. The system of claim 2 including first heat generating means in said curing station and second heat generating means in said drying station, said hot exhaust gases supplementing the heat generated by said first and second heat generating means.

8. The system of claim 7 wherein said first and second heat generating means comprise infrared fuel burners.

9. The system of claim 1 including in combination therewith,

a drying station along said conveyor means between said spray washing station and said coating station,

said conduit means conducting a first portion of said hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion,

first heat generating means in said curing station, and

second heat generating means in said drying station,

said hot exhaust gases supplementing the heat generated by said first and second heat generating means.

10. The system of claim 9 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.

11. The system of claim 9 wherein said first and second heat generating means comprise infrared fuel burners.

12. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, and conveyor means for conveying the articles between said stations, wherein the improvement comprises in combination therewith:

infrared fuel burners in said immersion conduit means, and

conduit means for conducting the hot exhaust gases from said infrared fuel burners in said immersion conduit means to said curing oven wherein said hot exhaust gases are utilized to cure the coating on the articles.

13. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, conveyor means for conveying the articles between said stations, and a drying station along said con veyor means between said spray washing station and said coating station, wherein the improvement comprises in combination therewith:

conduit means conducting a first portion of the hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion,

first heat generating means in said curing station, and

second heat generating means in said drying station,

said hot exhaust gases supplementing the heat generated by said first and second heat generated means.

14. The system of claim 13 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.

15. The system of claim 13 wherein said first and second heat generating means comprise infrared fuel burners. 

1. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, conveyor means for conveying the articles between said stations, and a drying station along said conveyor means between said spray washing station and said coating station, wherein the improvement comprises in combination therewith: conduit means for conducting the hot exhaust gases from said immersion conduit means to said curing oven wherein said hot exhaust gases are utilized to cure the coating on the articles and to said drying station to dry the articles prior to coating, said conduit means also conducting hot exhaust gases from said drying station to said curing station wherein the hot exhaust gases from said drying station are utilized to cure the coating on the articles.
 2. The system of claim 1 wherein said conduit means conducts a first portion of said hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion.
 3. The system of claim 2 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.
 4. The system of claim 1 including infrared fuel burners in said immersion conduit means, said hot exhaust gases being the exhaust gases of burners.
 5. The system of claim 1 including heat generating means in said curing station, said hot exhaust gases supplementing the heat generated by said heat generating means.
 6. The system of claim 5 wherein said heat generating means comprise infrared fuel burners.
 7. The system of claim 2 including first heat generating means in said curing station and second heat generating means in said drying station, said hot exhaust gases supplementing the heat generated by said first and second heat generating means.
 8. The system of claim 7 wherein said first and second heat generating means comprise infrared fuel burners.
 9. The system of claim 1 including in combination therewith, a drying station along said conveyor means between said spray washing station and said coating station, said conduit means conducting a first portion of said hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion, first heat generating means in said curing station, and second heat generating means in said drying station, said hot exhaust gases supplementing the heat generated by said first and second heat generating means.
 10. The system of claim 9 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.
 11. The system of claim 9 wherein said first and second heat generating means comprise infrared fuel burners.
 12. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, and conveyor means for conveying the articles between said stations, wherein the improvement comprises in combination therewith: infrared fuel burners in said immersion conduit means, and conduit means for conducting the hot exhaust gases from said infrared fuel burners in said immersion conduit means to said curing oven wherein said hot exhaust gases are utilized to cure the coating on the articles.
 13. An article finishing line and coating system including a spray washing station for washing the articles with a heated liquid, a tank for containing the washing liquid having an immersion conduit means therein through which hot gases are conducted to heat the washing liquid, a coating station for coating the articles, a curing station for curing the coating on the articles, conveyor means for conveying the articles between said stations, and a drying station along said conveyor means between said spray washing station and said coating station, wherein the improvement comprises in combination therewith: conduit means conducting a first portion of the hot exhaust gases from said immersion conduit means directly to said curing station and a second portion of said hot exhaust gases from said immersion conduit means to said drying station and then to said curing station in parallel relationship to said first portion, first heat generating means in said curing station, and second heat generating means in said drying station, said hot exhaust gases supplementing the heat generated by said first and second heat generated means.
 14. The system of claim 13 including exhaust blower means continuously discharging a portion of the heated gases from said curing station.
 15. The system of claim 13 wherein said first and second heat generating means comprise infrared fuel burners. 